Cell-mediated immune response to simian oncornavirus antigens in pregnant women

Tritiated thymidine incorporation into lymphocytes of 118 adult women was studied in the presence of mitomycin C-treated cells prepared from cell lines continuously producing Mason-Pfizer monkey virus (MPMV), baboon C-particle virus, or simian sarcoma virus (SSV) and in the presence of control cell lines documented for the absence of oncornaviruses. At the end of pregnancy, women who had 5-9 pregnancies showed a high frequency (53%) of specific positive responses to cells with MPMV antigens. The frequencies were 15% for pregnant women with smaller numbers of pregnancies and 3% for nonpregnant women with similar numbers of previous pregnancies as in the pregnancy group. None of these nonpregnant women had lymphocytes responding to stimulation by baboon C-virus antigens, but positive responses were obtained in 20 and 16% of the pregnant groups, respectively. No correlation was found between responses to MPMV or baboon C-virus antigens. Of 48 women (35 pregnant, 13 nonpregnant) who were tested for lymphocyte responses to SSV antigens, only 2 showed a positive response. The results indicated that two distinct antigens, related to MPMV and to baboon C-virus, may be expressed during pregnancy and may then induce a transient cell-mediated response.